It is known that wavelength discrimination can be accomplished by collecting broadband energy and then isolating specific narrow bands of interest and imaging them onto energy sensors. Narrow band flashes are readily detected because such signals will trigger an electrical current in only one channel of a state of the art device. The design approach usually adopted for such a device uses a simple catadioptric afocal telescope to collect and collimate the incoming energy and two dichroic beam splitters to isolate the wavelengths of interest. Typically this is followed by three separate imaging optics, three separate detectors and three separate detector coolers. It obviously would be advantageous to find an efficient technique that would combine the optical paths through a single imaging optic and place the three detectors on a single detector cooler.
Prior art devices typically utilize a large primary mirror that serves to collect and image the energy from extended sources. The energy is then recollimated to form a classical Newtonian Telescope. Three dichroic beamsplitters are then located in the collimated space separating the three selected wavelengths of interest and sending them to three separate imager optics and to three separate detectors. This solution is straightforward but results in a large, heavy and expensive system.
It was in an effort to improve upon systems of this type that the present invention was evolved.